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| 型号： | FSQ0765RQUDTU |
| 厂商： | Fairchild Semiconductor |
| 文件页数： | 14/19页 |
| 文件大小： | 0K |
| 描述： | IC CONV QUASI-RES 650V TO-220F-6 |
| 标准包装： | 400 |
| 输出隔离： | 隔离 |
| 频率范围： | 48kHz ~ 67kHz |
| 输入电压： | 9 V ~ 20 V |
| 输出电压： | 650V |
| 功率（瓦特）： | 90W |
| 工作温度： | -25°C ~ 85°C |
| 封装/外壳： | TO-220-6 成形引线 |
| 供应商设备封装： | TO-220-6L（成形） |
| 包装： | 管件 |
4.1 Overload Protection (OLP): Overload is defined as
the load current exceeding its normal level due to an
unexpected abnormal event. In this situation, the
protection circuit should trigger to protect the SMPS.
However, even when the SMPS is in the normal
operation, the overload protection circuit can be
triggered during the load transition. To avoid this
3R
R
OSC
PWM
LEB
250ns
S
R
Q
Q
Gate
driver
undesired operation, the overload protection circuit is
designed to trigger only after a specified time to
determine whether it is a transient situation or a true
overload situation. Because of the pulse-by-pulse
AOCP
FSQ0765R Rev.00
R sense
V OCP
2
GND
current limit capability, the maximum peak current
through the SenseFET is limited, and therefore the
maximum input power is restricted with a given input
voltage. If the output consumes more than this maximum
power, the output voltage (V O ) decreases below the set
voltage. This reduces the current through the opto-
coupler LED, which also reduces the opto-coupler
transistor current, thus increasing the feedback voltage
(V FB ). If V FB exceeds 2.5V, D1 is blocked and the 5μA
current source starts to charge CB slowly up to V CC . In
this condition, V FB continues increasing until it reaches
6V, when the switching operation is terminated, as
shown in Figure 29. The delay time for shutdown is the
time required to charge C FB from 2.5V to 6V with 5μA. A
20 ~ 50ms delay time is typical for most applications.
Figure 30. Abnormal Over-Current Protection
4.3 Output-Short Protection (OSP): If the output is
shorted, steep current with extremely high di/dt can flow
through the SenseFET during the LEB time. Such a
steep current brings high voltage stress on the drain of
SenseFET when turned off. To protect the device from
such an abnormal condition, OSP is included in the FSQ-
series. It is comprised of detecting V FB and SenseFET
turn-on time. When the V FB is higher than 2V and the
SenseFET turn-on time is lower than 1.2μs, the FPS
recognizes this condition as an abnormal error and shuts
down PWM switching until V CC reaches V start again. An
abnormal condition output short is shown in Figure 31.
V FB
FSQ0765R Rev.00
Overload protection
MOSFET
Drain
Current
Rectifier
Diode Current
Turn-off delay
I LIM
6.0V
V FB
2.5V
0
V o
D
Minimum turn-on time
1.2us
t 12 = C FB *(6.0-2.5)/I delay
0
output short occurs
t 1
Figure 29. Overload Protection
t 2
t
I o
0
FSQ0765R Rev. 00
4.2 Abnormal Over-Current Protection (AOCP): When
the secondary rectifier diodes or the transformer pins are
shorted, a steep current with extremely high di/dt can
flow through the SenseFET during the LEB time. Even
though the FSQ-series has overload protection, it is not
enough to protect the FSQ-series in that abnormal case,
since severe current stress is imposed on the SenseFET
until OLP triggers. The FSQ-series has an internal
AOCP circuit shown in Figure 30. When the gate turn-on
signal is applied to the power SenseFET, the AOCP
block is enabled and monitors the current through the
sensing resistor. The voltage across the resistor is
compared with a preset AOCP level. If the sensing
resistor voltage is greater than the AOCP level, the set
signal is applied to the latch, resulting in the shutdown of
the SMPS.
? 2008 Fairchild Semiconductor Corporation
FSQ0765RQ Rev. 1.0.1
14
Figure 31. Output Short Waveforms
4.4 Over-Voltage Protection (OVP): If the secondary-
side feedback circuit malfunctions or a solder defect
causes an opening in the feedback path, the current
through the opto-coupler transistor becomes almost
zero. Then, V FB climbs up in a similar manner to the
overload situation, forcing the preset maximum current
to be supplied to the SMPS until the overload protection
triggers. Because more energy than required is provided
to the output, the output voltage may exceed the rated
voltage before the overload protection triggers, resulting
in the breakdown of the devices in the secondary side.
To prevent this situation, an OVP circuit is employed. In
general, the peak voltage of the sync signal is
proportional to the output voltage and the FSQ-series
www.fairchildsemi.com
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